As is known in the art, noise can be created inside surface ships and submarines by various sources, such as fluid-filled regions. Exemplary fluid filled regions include ballast tanks, fuel tanks, fresh water tanks, and additionally for the case of a submarine, the free flood sail. Fluid filled regions are not, however, restricted to surface ships and submarines. Any fluid filled region that is subject to mechanical or acoustic excitation can create noise. If not sufficiently suppressed, such noise can pose an acoustic hazard.
A common noise source is sound emitted from suction and discharge pipes inside the fluid-filled regions. The frequency spectrum of the noise typically contains both broadband and tonal components. An example of a low frequency tonal component noise source is pump rotation (e.g., imbalance, impeller blade passing, and electrical harmonic distortion). After entering the fluid filled region via a pipe, a significant portion of this noise is transferred to the surrounding acoustic medium and structure, potentially creating a noise hazard.